This invention generally concerns an electronic system for controlling the power fed to light beam projectors, particularly of medium and high power, which use short arc lamps such as xenon and metal halide lamps. More specifically, the invention relates to an electronic control system which enables both a stroboscopic effect and a dimmer effect to be obtained with said type of lamp.
The known art teaches that with this type of lamp a stroboscopic effect, ie, a rapid variation in light intensity, and a dimmer effect, ie, an attenuation in light intensity, can only be obtained by using mechanical means.
To achieve a stroboscopic effect, devices are known comprising vanes which are made to oscillate in a plane perpendicular to the light beam so as to obscure the beam. The maximum vane oscillation frequency which can be achieved-with devices of this type is of the order of 9 Hz for small and medium dimension projectors. As the projector dimensions increase the maximum vane oscillation frequency decreases. The ideal frequency at which the human eye perceives a stroboscopic effect lies between 7 and 10 Hz, which values can hence be approached only by small dimension projectors. In contrast, to achieve a dimmer effect, movable mechanical shutters are used located in front of the light beam in such a manner as to be able to partially or completely intercept their light flow.
A drawback of such shutters is that they are unable to completely intercept the light beam for a lengthy period. This is due to the considerable heat which develops on the shutter surface, so deforming it and making the shutter unusable.
An object of the invention is to overcome said drawbacks within the framework of a rational and economical solution.
The invention attains this and further objects by providing an electronic system for controlling the power fed to short arc lamps able to generate and control light effects such as a dimmer effect and a stroboscopic effect.
The electronic control system of the invention is able to control the instantaneous power transmitted to the lamp and to vary it with such a frequency as to achieve a stroboscopic effect at the ideal frequency perceivable by the human eye, or to achieve a dimmer effect.
More specifically, said system comprises an electronic power unit of switching type controlled by a feedback system which causes it to deliver power on the basis of a reference value which can oscillate between zero and the maximum allowable lamp power. Said reference value can be set by the operator or be generated by a suitable pulse generator.